1. Field of the Invention
The present invention relates generally to devices for removing smoke, dust and fumes from the air, and more particularly to a novel modular electrostatic precipitator (ESP) system having among its features the employment of modular ionizer/collector cells that facilitate mechanical nesting of individual cell modules, fault detection at the individual cell level, and a high voltage source for each modular ionizer/collector cell so as to enhance overall system air cleaning efficiency.
2. Description of Related Art
Conventional two-stage ESPs are energized by a power supply source having a single, alternating current (AC) input voltage and a single or dual, direct current (DC) output voltage. Input voltages can range from 24 v to 240 v, and output voltages can range from 3 Kv to 15 Kv. A single output voltage power supply electrically connects the same high voltage potential to the ionization and collection section of an ESP. A dual output voltage power supply provides different levels of high voltage potential to the ionization and collection section, with the ionization section approximately twice the voltage level of the collection section. For example, a dual output voltage power supply that generates a high voltage level of 12 Kv to the ionization section will supply approximately 6 Kv to the collection section.
Each power supply or combinations of power supplies in conventional ESP systems are located in an enclosure, separate from the ionization and collection section of the ESP. These enclosures can be in proximity to the ESP, for example, on the ESP access panel, or the enclosure can be remote mounted a distance from the ESP. High voltage electrical connections between power supply and ESP are made by an insulated cable or wire, sized to carry the maximum electrical load. Electrical conduit is required to shield and protect the high voltage cable or wire when the power supply enclosures are mounted in a remote location. Once connected to the ESP, various conductive devices such as springs, plungers, cables, wires, or buss bars transfer high voltage between multiple ionization/collection sections (known as a cell or module). Each device is isolated from ground by a non-conductive material such as a fiberglass reinforced plastic (FRP) or ceramic. The cell-to-cell high voltage connections are located at each end of the cell and are shielded or baffled from the air stream to prevent contamination or corrosion. A tie rod or expanded tube is conventionally used to transfer high voltage through an individual cell. A series of individual cells are trained together to form a tier of cells. Each cell on a tier slides on a rail. Multiple tiers can be stacked vertically to complete the final ESP configuration.
The relationship between the current draw of a single cell, typically measured in milliamps, and the total current capacity of the power supply determines the number of cells that can be powered by one power supply. For example, a power supply rated for 10 milliamps can power 5 cells that draw 2 milliamps each. The number of cells or modules required for an ESP is dependent on the volume of air being moved in cubit feet per minute (CFM) and the desired efficiency (percentage of particles removed from air). After determining the number of cells required for an ESP based on this criteria and the total current draw for the cells, the number of power supplies required can be determined.
There are several disadvantages to the aforedescribed prior ESP and power supply arrangement. For example, the larger the ESP, the more difficult and expensive the high voltage wiring becomes between the power supplies and the cells. Power supply enclosure quantity, size and expense increase with the increase in size of the ESP. High voltage connection points and transfer devices required increase in number with increasing size of the ESP, thereby adding additional expense. Each high voltage connection point or transfer device must be electrically sound. Weak high voltage connections result in decay and failure of surrounding materials caused by arcing or corona stress. On conventional ESP""s, an operating status light is used as a diagnostic device. For example, an LED is frequently provided as part of the power supply circuitry. Under normal operating conditions the LED will illuminate, indicating that the ESP and power supply are functioning properly. In a fault condition, however the LED does not illuminate so that trouble-shooting and isolating individual component failure becomes more difficult because the only device used for detection is part of the power supply. For example, the LED, being connected in circuit with the failed power supply, will not indicate which cell, if any, has a problem. On a conventional electrostatic precipitator, one power supply energizes multiple ionizer/collector cells. Under this arrangement, a power supply failure would result in the loss of power to a group of cells and greatly reduce the air cleaning efficiency of the electrostatic precipitator. As an added expense, volt and amp meters can be provided in addition to the operating status light, for increased operational monitoring of the ESP. On ESP""s that utilize a rail system configuration, clearance for sliding of the cell is provided between the sides of the rail and cell. This clearance, usually one sixteenth to one quarter inch, generally creates misalignment between cells in a tier. Any high voltage connections between cells must compensate for the misalignment.
One of the primary objects of the present invention is to overcome the aforementioned problems in known modular electrostatic precipitators (ESPs) by eliminating the high voltage components required for installation, and providing fault detection at the individual cell level in a cost-effective manner so as to enhance ESP performance.
A more particular object of the present invention is to provide a system of modular ESP cells wherein the cells can be supported in tiers and a power supply is united into the body of each cell so that all high voltage components are contained and isolated within the cell, thereby eliminating high voltage connections between cells, high voltage cabling between the ESP and a remote mounted power supply, and power supply enclosures.
Another object of the invention lies in providing each ESP cell with an alarm circuit and status indicator display for monitoring the normal operation of each cell, and wherein a tier of cells connects in series the alarm circuit from each cell, and a status indicator light monitors each tier of cells so that under normal operating conditions, a signal energizes each tier alarm circuit and illuminates the tier status indicator light.
In accordance with one feature of the invention, the alarm circuit energizing signal is carried through the tier to each cell so that when a fault is detected in a cell or power supply, for example, if high voltage plates in the collector section of a cell are shorted to ground, the alarm circuit for that cell will open or become de-energized and the cell status indicator will not be illuminated. Such open circuit condition to a tier of ESP cells causes the status indicator light for the tier to become non-illuminated.
In accordance with another feature of the invention, the status circuit also detects whether input power is connected to the cell power supply, and monitors cell arcing.
In accordance with another feature of the invention, a tier auxiliary status port is provided whereby connection to external devices for monitoring tier status can be effected.
Still another feature of the ESP modules in accordance with the invention lies in the provision of a low voltage (24 v-240 v) input power distribution network that utilizes a radial float xe2x80x9cblind matexe2x80x9d connector (RFC) that is also used in the cell status circuit and is particularly suited for conventional ESP applications that require low voltage electrical connections between cells that may become misaligned in a support frame.
In accordance with the invention, the ESP cell modules are adapted for mechanical nesting in a manner to correct misalignment for electrical connections between cells when placed in series on a support rack, and when nested provide sufficient air baffling between cells to protect exposed high and low voltage electrical components. To this end, end plates on the modular ESP cells are adapted for end-to-end nesting so as to form a sealed cavity in which electrical components such as power supplies can be enclosed. The sealed cavity also serves as a baffle, forcing air-borne particles through the ionization and collection sections of the cell and preventing bypass between cells.